The present invention relates to control devices for nail hitting of pneumatic nail guns, and particularly to a high pressure air control valve disposed in a main air flow passage between a trigger valve and a main valve.
Generally, when a nail gun is used for nailing a work part, such as a washer, via its through hole to a work piece a back end of the nail is usually exposed onto the work piece so as to fix the work part. In order to selectively control the nail hitting in light of the different work parts, a control device is usually arranged in the main air flow passage between a trigger valve and a main air valve. A knocking base positioned below a bottom end of a safety slide pole abuts against the work part for detecting a height of the through hole of the work part. So the high pressure air is controlled to open the main air valve to hit nails.
One kind of pneumatic nail gun with control device for nail hitting is described in US Patent Publication No. 20070075113. The pneumatic nail gun has a cam follower driven by a movable portion, and a body portion is capable of being blocked or released by the cam follower. The body portion can be blocked or released by the movable portion to control the high pressure air to open the main air valve to hit nails. However, the cam follower is exposed between the body portion and the movable portion. The cam follower will accumulate dust to affect the operation performance of the nail gun. This nail gun expressly has a complex structure.
Further, a pneumatic nail gun with a control device providing a safety design on the hitting process is described in Taiwan Patent Publication No. M312401. The nail gun has a hollow valve bolt being driven or released by a safety slide pole, and a valve cover which can exhaust the high pressure air to the outer atmosphere through opening or closing the main air flow passage controlled by the valve bolt. The safety slide pole is first driven to move up to block the valve bolt. The high pressure air in the main air flow passage is then exhausted to the outer atmosphere by pulling the trigger. The main air valve can be controlled to hit nails. However, the passage configuration between the hollow valve bolt and the valve cover is complicated. There is not enough air being collected in the main air chamber and the main air flow passage. The stability is not good.